Doyle last month approved funding of a $375 million institute for stem cell research at the University of Wisconsin-Madison and the state's commerce department is spending $5 million to attract research firms to Wisconsin.
A letter sent Monday by Milwaukee Archbishop Timothy Dolan and Madison Bishop Robert Morlino on behalf of the state Catholic conference said stem cell research "further diminishes human embryos to mere commodities," the Milwaukee Journal Sentinel reported Thursday.
Doyle, a Democrat and a Catholic, has made stem cell research a keynote of his re-election campaign, saying cutting-edge research at the state university would create jobs and possibly find breakthroughs for treatment of illnesses like Parkinson's disease.
His opponent in the governor's race, U.S. Rep. Mark Green, R-Wis., also is Catholic.
Ohio crash that killed two caught on camera [VIDEO]
Wisconsin business offering 'therapeutic cuddling' forced to close